In lung cancer, bombesin/gastrin releasing peptide (BB/GRP) is an autocrine growth factor. GRP receptors are present on NCI-H1299 cells. Previously we found that BB caused phosphatidylinositol turnover, elevation of cytosolic Ca2+, phosphorylation of mitogen activated protein kinase and increased expression of c-fos mRNA after addition to NCI-H1299 cells. Also BB caused increased tyrosine phosphorylation of focal adhesion kinase (FAK) and paxillin after 1 min. The half maximal effective dose for BB to cause tyrosine phosphorylation of FAK was 10 nM. Similarly GRP and GRP14-27 but not GRP1-16 caused tyrosine phosphorylation of FAK. The ability of BB to cause tyrosine phosphorylation of FAK was inhibited by the GRP receptor antagonist BW2258U89. These results suggest that GRP receptors may activate a guanine nucleotide binding protein resulting in the tyrosine phosphorylation of FAK. FAK activation may facilitate the growth of lung cancer cells. Also, neuromedin B (NMB) and bombesin receptor subtype-3 (BRS-3) receptors are present on NCI-H1299 cells. BRS-3 receptors were activated by the synthetic peptide (FAFN)BB6-14. (FAFN)BB6-14 caused phosphatidylinositol turnover, elevation of cytosolic Ca2+, phosphorylation of mitogen activated protein kinase, activation of elk-1 and increased expression of c-fos mRNA after addition to NCI-H1299 cells. The actions of (FAFN)BB6-14 were blocked by substance P antagonists but not BW2258U89 or PD168638, a NMB receptor antagonist. These results suggest that the signal transduction mechanisms for BRS-3 receptors are similar to those of GRP receptors.